Question 967445
Let the length be 3x.
Then the width is (x+3).
area=length*width
3x(x+3)=84
x(x+3)=28
x^2+3x-28=0
x^2+7x-4x-28=0
x(x+7)-4(x+7)=0
(x-4)(x+7)=0
x=4 is the only positive solution.
The length is 12 metres.
The width is 7 metres.